Radio frequency parallel bonding



Jan. 13, 1948. v w, MANN r AL 2,434,573

I RADIQ FREQUENCY PARALLEL BONDING I Filed June 26, '1942 (111.4; I I INVENTORS GEORGE F. RUSSELL. BYJULIUS W-MANN ATTO RNEYS Patented Jan. 13, 1948 o'irlca RADIO FREQUENCY PARALLEL BONDING Julius W. Mann and George F. Russell,

Tacoma, Wash.

Application June 26,1942, Serial No. 448,678

'5 Claims. (01. 154-126) The present invention relates to improvements in radio frequency bonding, and it consists of the combinations, constructions and arrangements hereinafter described and claimed and in the steps hereinafter set forth.

An object of our invention is to provide a new method of bonding two or more materials which differs from the method of bonding used and described in a copending application of George 1-. Russell, Serial No. 367,147, on a Plywood process, filed November 25, 1940. In the copending case a plurality of pieces of veneer are placed one above the other and are secured to each other by glue or other adhesive material. The bonding of the glue to the veneer is accomplished by using a radio circuit and causing the high frequency field lines of force generated by the circuit to pass through the veneer and the glue for raising the temperature of the glue to a'point-where'eflective bonding takes place.

Our present invention differs from the copending case in that the high frequency field lines of force are set up in paths which are substantially parallel to the planes of the glue lines which bind the veneer layers together. The glue lines or planes could extend at angles to the paths of the high frequency field lines of force up to apoint where they are almost at right angles to their direction. In other words, we wish to include the bonding of two materials by high frequency field lines of force where the abutting surfaces of the materials form one or more planes that extend either parallel to the normal paths of the high frequency field lines of force or up to an angle which is slightly less than right angles to the normal path taken by the high frequency field lines of force. Although we contemplate using the method for bonding a plurality of veneers to each other by glue or other adhesive material to form plywood, it is as easily feasible to bond other similar or dissimilar materials together whether a bonding material is used between the layers or not.

Where bonding is accomplished by passing high frequency field lines of force generated by a radio circuit through the veneers in a direction at right angles to the planes of the bonding materials, the layers of veneer act as dams or obstructions to the high frequency field lines of force, thus necessitating a higher source of power to effect the bonding because the heat created by the friction of the passage of the high frequency field lines of force must heat the wood or other material as well as the glue lines. This limits the number of layers of material which may be bonded together at any one time. One characteristic of heating by lines of force generated by a radio circuit in a high frequency field, is that heat is produced at a greater rate in the more conductive materials than in the less conductive materials. In thi respect heating by a radio circuit is unique. by causing the high frequency field lines of force to pass parallel to the glue lines or planes, the number of layers of material may be greatly increased because the series\of dams or obstructions created by the layers of material are removed.

The new method is especially adapted for the batch bonding of veneers of plywood.

Other objects and advantages will appear in the following specification, and the novel features of the device will be particularly pointed out in the appended claims.

Our invention is illustrated in the accompanying drawing forming a part of this application, in which:

Figure 1 is a perspective view of a plurality of plies of veneer placed between the electrode plates, the plates being spaced from the stack of plywood for purpose of clarity;

Figure 2 is an end elevation of Figure 1 shown on a smaller scale and with the parts arranged in juxtaposition/for the bonding of the material;

Figure 3 illustrates the method when used for bonding two or more materials where the glue line or plane extends at any angle other than one which is parallel to the planes of the electrode plates; and

Figure 4 is a view illustrating the present practice of batch bonding of plywood by the use of high frequency field lines of force generated by a radio circuit passed through the veneer layers and the glue lines, where both lie substantially perpendicular to the normal path of the high frequency field lines of force.

In carrying out our invention we show in Figure 4 the usual method and will briefly describe this before setting forth our improved method. A stack of veneer indicated generally at A in Fig.- ure 4 has a plurality of sheets or pieces of veneer indicated at I with glue lines or planes 2 placed between adjacent layers of veneer.v At the top and bottom of the stack of veneer, electrode plates 5 and 6 are arranged on the outer sur-' When the bonding is accomplished- 3 filed August 20, 1941, now abandoned. It is obvious that any other type of high frequency radio circuit may be used.

In the operation of the method shown in Figure 4, the high frequency field lines of force will pass between the plates 5 and 6 in paths which are substantially perpendicular to the glue lines 2. The high frequency field lines of force will increase the internal temperature of the mass and the glue lines or planes to a point where bonding of the veneers will take place. As already stated, the diificulty of such a method is that the number of veneers which may be bonded together i limited to the power of the radio circuit and the time cycle since the high frequency field lines of force must penetrate and generate heat in the entire number of veneer layers as well as the glue lines, therebetween. 1

By placing the electrodes at the sides of the stack of veneers instead of at the top and bottom as shown in Figure 4, the high frequency field lines of force will parallel the planes of the glue lines rather than be perpendicular thereto. This is the gist of our present invention and is the vital point of difference from the method shown in Figure 4. We have discovered that the glue lines provide low resistance paths between the electrodes along and through which the high fre quency filed lines of force will pass more readily than through the veneers and the glue lines. As stated above, one characteristic of radio frequency heating is that heat is produced at a greater rate in the more conductive materials than in the less conductive materials. In the method shown in Figure 4, the high frequency field lines of force must pass through veneer layer dams whereas in our method they need not. This improved method primarily raises the tem-' perature of the glue lines to effect a bonding of the layers of veneer. The number of layers of veneer to be bonded may be increased and this will permit beams and large pieces of timber to be made of plywood which is not possible at present.

In Figure 1 we show a stack of plywood B which is formed of a number of layers of veneer 8. The glue lines or planes are indicated at 9. The caul boards and H are placed at the sides of the stack or perpendicular to the glue lines illustrated. The electrode plates l2 and I3 are separated from the plywood stack B by the caul boards. The caul boards are for the purpose of insulating the damp glue lines so that they will not contact the charged electrode plates causing low resistance paths to short out the radio fre: quency field. An air space between the package and the electrodes may be used in lieu of cauls. should it be desired under certain production conditions. Figure 2 shows the parts of Figure l assembled together with the plates l2 and I3 electrically connected to an inductance l4. The inductance in turn forms a portion of a high frequency radio circuit such as that shown in our copending application, Serial No. 407,530. The top and bottom of the plywood stack B has pressure blocks I5 and I6 of a non-conducting material applied thereto for holding the layers of veneer together under pressure during the bonding operation.

In the operation of the method illustrated in Figure 2, the pressure is applied to the blocks l5 and I6 for forcing the veneer together before, after or during which the high frequency field of force is established between the plates 12 and I3. This high frequency field will comprise lines 4 of force which parallel the glue lines or planes since these planes extend perpendicular to the plane of the electrodes. The layers of veneer 8 do not act as substantial dams or obstructions to the displacement currents resulting from the high frequency field lines of force because the lines will parallel the damp glue lines which parallel the planes of the veneer, seeking all the while the paths of least resistance. We have shown nineteen plies in Figures 1 and 2 although we do not wish to be confined to this number since it may be increased or decreased at will. The bonding is more rapidly accomplished because, with electron dlsplacement parallel through the glue lines, quicker penetration results since the glue line is heated more rapidly than usual. The only material the high frequency field lines of force pass through before reaching the glue lines are the cauls, or the air gap. Elimination of low limits on the thickness of the mass or package of veneer which may be bonded is possible. The parts are so designed that the package may be readily loaded in the device carrying the electrode plates and unloaded therefrom with a minimum of eiifort, and without removing or disturbing the electrode placement. Another advantage apparent with the use of this new process is the requirement of less radio frequency power per glue line since heatis developed at a greater rate in the glue line because it is more conductive than the veneer. The air space between the electrodes andthe package adds a distinct advantage under some circumstances because it allows a more even distribution of the high frequency field lines of force not possible where the electrodes are above or below, or directly connected to the sides of the package being treated. Another very distinct advantage of this method of parallel gluing is that it allows a very small change in frequency while the load is under compression and changes take place in density and thickness of the package because-the plates constituting the electrodes do not have to follow the compression of the load. v

Although we mention the bonding of plywood, it is obvious that any material may be bonded such as brake linings to brake shoes, etc. Our process contemplates the gluing of any materials together whether or not the materials are the same. A bonding agent such as glue could be used or in some instances the materials themselves may be bonded together when placed in contact with each other and subjected to penetration by lines of force of a high frequency field.

In Figure 3 we illustrate a glue line I1 extending at an angle to the electrode plates l8 and it which is less than perpendicular. Two pieces of material shown at 20 and 2| are separated from each other by a glue line 11 such as would be found in a scarfed joint. The glue line may extend at an angle where it will not contact with the caul boards 22 and 23. Such an angle is indicated by the broken lines 24 indicating another glue line or plane.

The operation of this form of device is the same as-that shown in Figure 2. The inductance 25 is connected to the plates l8 and I9 and to a radio circuit, not shown. The high frequency field lines of force will pass between the plates and since the glue line extends at an angle to the plates, the displacement currents will move along the glue lines H or 24 more readily than they will pass through the pieces 20 and 2|. The result is that a bonding of the two materials takes place without the use of so much power. The glue line 24 extends at an angle slightly off from one that parallels the plates or electrodes. We are illustrating this angle because we wish to cover the use of a glue line at any angl'e which is not par-' We have set forth the electrode plates will speed up the bonding of the parts by the setting of the glue. The nearer the glue lines approach an angle perpendicular to the planes of the electrodes, the more rapid is the setting of the glue.

We claim:

1. The herein described step in a. method of setting adhesives placed between pieces of material by the penetration of radio frequency lines of force which comprises placing the material with the adhesive in the radio frequency field so that the field lines of force parallel the planes defined by the adhesives so that a concentration of lines of force will pass through the adhesives for quickly drying them.

2. The process of Joining surfaces which comprises placing the surfaces to be Joined together with a film of adhesive therebetween and placing the composite parts between fiat parallel electrodes connected to a source of high frequency electrical current, the surfaces and the adhesive film plane forming an angle with the electrodes of nine y d grees rather than extending parallel therewith.

3. The herein described method of heating an adhesive plane placed between abutting pieces of material to be joined by using high frequency electricity to establish electrostatic lines of force which comprises placing abutting pieces of material with the adhesive plane therebetween in the established field of force in a position where the adhesive plane will parallel the lines of force of the electrostatic field,

4. Theherein described step in a method of heating an adhesive plane placed between abutting pieces of material to be joined by means of a high frequency field between spaced electrodes which comprises placing abutting pieces of dielectric material surfaces with adhesive therebetween in said field with the plane ofthe adhesive extending parallel to a straight line connecting the electrodes at their closest points.

5. The herein described step in a method of setting adhesive by the penetration of radio frequency lines of force, the adhesive being placed between the confronting surfaces of JuXtaDOsitioned pieces of material, which comprises placing the material with the adhesive in the radio frequency field so that the field lines of force extend entirely across the pieces of material between opposite edges thereof and parallel to a plane defined by the adhesive so that a concentration of lines of force will pass completely through the adhesive and between said opposite edges for quickly drying the adhesive.

JULIUS w. MANN.

GEORGE I". RUSSELL.

REFERENCES map The foilowingreferences are of record in the file of this patent:

UNITED STATES PATENTS 

